The present invention relates to an improvement of a screw press apparatus to be used for dehydration such as of sludge, and particularly, it relates to a structure for enhancing a filtering function of a screw press and a structure for eliminating blocking of a screen.
A typical screw press apparatus has an outside tube and a screw shaft disposed in the outside tube. Raw liquid is fed between the outside tube and the screw shaft, ad is dehydrated and compressed by rotation of the screw shaft, to be separated into solid and liquid.
As the raw liquid is concentrated, getting sludgy, and is further dehydrated, forming a cake, the load of a driving device for rotating the screw shaft increases, so that the cake may not be compressed sufficiently.
The outside tube is covered with a metallic screen low of pressure resistance. In the case where adhesive foul water or the like is dehydrated, high pressure resistance is required, and thus the metallic screen is reinforced with a ring, a flange or the like. Moreover, since the mesh of the metallic screen, which processes adhesive slurry, is generally fine, the screen tends to be clogged and thus it is necessary to clean the screen.
The clogged screen is cleaned by a brushing or by a blowing with compressed air. However, as it is difficult to uniformly apply a brush and a blow of compress air to the screen due to the presence of reinforcing flange or the like, and as the screen has uniformly fine meshes, there is a possibility that the screen may not be cleaned sufficiently.
A principal object of the present invention is to provide a screw press apparatus in which the structure for supplying raw liquid and the structure of a screen are improved, so that a dehydrating process exhibits an enhanced performance, and the screen has a reduced load thereon in a dehydration process for sludge, effecting a facilitated sufficient elimination of a blocking of the screen.
Another object of the invention is to provide a control device implemented for load reduction to be effected on a rotary drive for a screw shaft in a dehydration process for slurry.
To achieve the object, a screw press apparatus according to a first aspect of the invention comprises a first and a second frame (3, 4) in opposition to each other, an outside tube (5) having a screen (8) on its peripheral surface, a screw shaft (6) having a spiral screw blade (13), a supply pipe (16) for supplying raw liquid in the screwshaft (6), and a cleaning pipe (34) for ejecting cleaning water to the screen (8). The outside tube (5) is supported on the frames (3, 4). The screw shaft (6) is inserted through the outside tube (5) and is supported rotatably on the frames (3, 4). The supply pipe (16) is fixed to one end (6a) of the screw shaft (6) supported on the first frame (3). The screen (8) is disposed between the frames (3, 4) and has a plurality of fine holes (74). The screw shaft (6) and the screen (8) define a cylindrical space (70) continuously extending from an upstream region (71) at a side of the first frame (3) to a downstream region (72) at a side of the second frame (4). The screw blade (13) is projected from the screw shaft (6) into the cylindrical space (70) and continuously extends from the upstream region (71) to the downstream region (72). An opening (73) for supplying the raw liquid from the supply pipe (16) to the upstream region (71) of the cylindrical space (70) is formed in the screw shaft (6). An outer peripheral surface of the screw shaft (6) and an inner peripheral surface of the screen (8) have a relative distance therebetween, which decreases from the upstream region (71) towards the downstream region (72). Raw liquid fed from the opening (73) to the upstream region (71) is pressurized and carried towards the downstream region (72) by the screw blade (13), while being separated into filtrate allowed to flows through the fine holes (74) out of the screen (8) and a cake allowed to move in the cylindrical space (7), to be discharged from the downstream region (72). Sizes of the fine holes (74) of the screen (8) decrease gradually from the upstream region (71) towards the downstream region (72).
According to the above arrangement, the raw liquid fed from the opening (73) of the screw shaft (6) to the upstream region (71) of the cylindrical space (70) is carried towards the downstream region (72) by the screw blade (13). The relative distance between the outer peripheral surface of the screw shaft (6) and the inner peripheral surface of the screen (8) corresponds to a radial width of the cylindrical space (70). As the width decreases from the upstream region (71) towards the downstream region (72), the raw liquid is carried and simultaneously pressurized gradually, and the filtrate flows through the fine holes (74) out of the screen (8), to be concentrated. R raw liquid in the cylindrical space (70) becomes sludge in an intermediate stage, and is further concentrated to form the cake, to be finally discharged from the downstream region (72). Namely, raw liquid is separated into the filtrate which flows out of the fine holes (74) and the cake which is discharged from the downstream region (72).
Since the opening (73) for supplying raw liquid is formed in the screw shaft (6), the raw liquid is fed in free of influences from the screw blade (13). Therefore, even if soft flocs cohered by a cohesive agent is mixed in the raw liquid, the flocs are hardly broken, assuring a dehydration performance free of damages.
The sizes of the fine holes (74) of the screen (8) decrease gradually from the upstream region (71) towards the downstream region (72). On the contrary, the pressure acting on the raw liquid in the cylindrical space (70) rises gradually from the upstream region (71) where the radial width is large towards the downstream region (72) where the radial width is small. For this reason, in the upstream region (71) low of pressure, the filtrate flows out of the large fine holes (74) satisfactorily. Moreover, since the fine holes (74) become smaller gradually towards the downstream region (72) high of pressure, where sludge is changed to a cake, the sludge hardly flows out of the fine holes (74) and thus only the filtrate outflows satisfactorily. Therefore, raw liquid is separated into the filtrate and the cake satisfactorily, and thus the filtering performance is improved.
In the case where the screen (8) is blocked, cleaning water is ejected from the cleaning pipe (34) to the screen (8), and thus the screen (8) is reusable.
A second aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a scraper (14) fixed to the screw blade (13). The scraper (14) is continuously extends from the upstream region (71) to the downstream region (72) and contacts elastically on the screen (8).
According to this arrangement, since sludge is scrapped off from the fine holes (74) of the screen (8) periodically by the scraper (14), the blocking of the screen (14) is prevented previously in a whole region covering from the upstream region (71) to the downstream region (72).
The scraper (14) extends continuously from the upstream region (71) to the downstream region (72), and in comparison to a case where a scraper is disposed partially, the positioning is facilitated, with a reduced tendency to have positional deviation.
A third aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a claw (28) fixed to the supply pipe (16), a first movable claw (31) provided on the outside tube (5) in correspondence to the claw (28), a first spring (30) for biasing the first movable claw (31), a first guide surface (75) provided on at least one of the claw (28) and the first movable claw (31), to work when the screw shaft (6) rotates in a forward direction, a stopper (33) fixed to the second frame (4), a second movable claw (78) disposed on the outside tube (5) in correspondence to the stopper (33), a second spring (77) for biasing the second movable claw (78), and a second guide surface (79) provided on at least one of the stopper (33) and the second movable claw (78), to work when the screw shaft (6) rotates in a reverse direction. The outside tube (5) is supported rotatably on the frames (3, 4). The first spring (30) biases the first movable claw (31) within a range where the claw (28) moves according to the rotation of the screw shaft (6). The second spring (77) biases the second movable claw (78) within a range where the stopper (33) moves according to a rotation of the outside tube (5). When the screw shaft (6) rotates in the forward direction, the first movable claw (31) is adapted by a guiding of the first guide surface (75), to move out of the moving range of the claw (28) against the biasing force of the first spring (30),allowing a relative rotation of the outside tube (5) with respect to the screw shaft (6), and the second movable claw (78) is adapted by the biasing force of the second spring (77), to engage with the stopper (33), preventing the relative rotation of the outside tube (5) with respect to the frames (3, 4). As a result, the screen (8) is held in a stopped state relative to the frames (3, 4), and raw liquid is pressurized and carried from the upstream region (71) to the downstream region (72). When the screw shaft (6) rotates in the reverse direction, the first movable claw (31) is adapted by the biasing force of the first spring (30), to engage with the claw (28), preventing the relative rotation of the outside tube (5) with respect to the screw shaft (6), and the second movable claw (78) is adapted by a guiding of the second guide surface (79), to move out of the moving range of the stopper (33) against the biasing force of the second spring (77), allowing a relative rotation of the outside tube (5) with respect to the frames (3, 4). As a result, the outside tube (5) rotates integrally with the screw shaft (6). According to this arrangement, in a normal filtering operation, the drive (25) rotates the screw shaft (6) in the forward direction. As the screw shaft (6) is forward rotated, the first movable claw (31) is not engaged with the claw (28), allowing a relative rotation of the outside tube (5) to the screw shaft (6), and the second movable claw (78) engages with the stopper (33), preventing the relative rotation of the outside tube (5) to the frames (3, 4). Thereby, with the screen (8) in a stopped state relative to the frames (3, 4), the screw blade (13) rotates relative to the screen (8), and raw liquid is carried under pressure, from the upstream region (71) to the downstream region (72).
In a cleaning operation, the drive (25) makes the screw shaft (6) rotate in a reverse direction. As the screw shaft (6) is reverse rotated, the first movable claw (31) engages with the claw (28), preventing the relative rotation of the outside tube (5) to the screw shaft (6), and the second movable claw (78) is not engaged with the stopper (33), allowing a relative rotation of the outside tube (5) to the frames (3, 4). Thereby, the outside tube (5) and the screen (8) are rotated integrally with the screw shaft (6), and compressed sludge in the cylindrical space (70) is fed back. Under such a condition, cleaning water is ejected from the cleaning pipe (34) to the screen (8), so that a whole peripheral region of the screen (8) is well washed to be reusable.
A fourth aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a pump (59) for supplying the raw liquid, a supply path (60) for interconnecting the supply pipe (16) and the pump (59),and a coagulant mixing tank (39) provided in the supply path (60). The coagulant mixing tank (39) has a tank body (81), an upper cover (82), a gland box (48), a gland packing (46), a seal pipe (51), and an agitation shaft (40). The tank body (81) has an opening (83), a raw liquid inlet (84), a raw liquid outlet (44), and a cohesive agent supply opening (86). The raw liquid outlet (44) is disposed below the opening (83). The raw liquid inlet (84) and the cohesive agent supply opening (86) are disposed below the raw liquid outlet (44). The opening (83) is covered with the upper cover (82). The upper cover (82) has a through hole (88) into which the gland box (48) is fitted. The agitation shaft (40) is inserted through the gland box (48). The glad packing (46) performs a sealing between the agitation shaft (40) and the gland box (48). The agitation shaft (40) has an agitating blade (42) disposed below the raw liquid outlet (44) in the tank body (81). The sealed pipe (51) extends from a lower end of the gland box (48) to cover the agitation shaft (40). A lower end (51a) of the sealed pipe (51) is dipped in raw liquid in the tank body (81).
According to this arrangement, supplied raw liquid from the pump (59) inflows via the raw liquid inlet (84) to the tank body (81). In the tank body (81), raw liquid is mixed by the agitating blade (42) with the cohesive agent supplied from the cohesive agent supply opening (86). By the mixing of raw liquid and cohesive agent, there are produced flocs. Raw liquid containing the flocs is sent from the raw liquid outlet (44) to the supply pipe (16).
As pulsatory actions generated at the pump (59) are moderated with compressive air in the tank body (81), flocs in raw liquid are supplied via the supply pipe (16) into the cylindrical space (70), without destruction.
Further, the opening (83) of the tank body (81) is closed by the upper cover (82), the gland box (48) is fitted in the through hole (88) of the upper cover (82), and the agitation shaft (40) is inserted through the glad box (48). Between the agitation shaft (40) and the glad box (48) is sealed with the glad packing (46), and the lower end (51a) of the shield pipe (51) extending from a lower end of the glad box (48) to cover the agitation shaft (40) is submerged in raw liquid in the tank body (81). Therefore, inside the tank body (81) is kept sealed, so that air in the tank body (81) can exhibit a desirable compression property.
Incidentally, the pressure for charging raw liquid into the screw press may be set to 0.05 to 0.5 kg/cm2 (approx. 4.9 to 49 kPa), for raw liquid to be free of occurrence of leakage as well, and to achieve a deodorizing effect even in the case of a processing such as of sewage.
A fifth aspect of the invention provides a crew press apparatus depending from the first aspect, which further comprises a drive (25) for driving the screw shaft (6), a torque detector (52) provided for the drive (25), and a control unit (89) for controlling the drive (25) in accordance with detected torque detected by the torque detector (52).
According to this arrangement, as the imposed load on the drive (25) varies with a changed state of raw liquid in the cylindrical space (70), the detected torque by the torque detector (52) changes. The control unit (89) is adapted to then control the drive (25) in dependence on a variation of detected torque. Therefore, raw liquid in the cylindrical space (70) has a stable state, giving a stable state to the cake to be discharged.
A sixth aspect of the invention provides a screw press apparatus depending from the fifth aspect, in which the control unit (89) has a comparator (53) and a controller (54). The drive (25) comprises a variable speed motor. The reference torque region having a specified range is set in the comparator (53).
The comparator (53) compares the detected torque with the reference torque region, and when the detected torque does not reach the reference torque region, the comparator (53) outputs a speed decrease request signal to the controller (54), and when the detected torque exceeds the reference torque region, the comparator (53) outputs a speed increase request signal to the controller (54). When the controller (54) receives the speed decrease request signal, the controller (54) has the drive (25) decrease in speed for a specified time, and when the controller receives the speed increase request signal, the controller (54) has the drive (25) increase in speed for a specified time.
According to this arrangement, when the moisture content of a cake is increased with insufficient dehydration of sludge in the cylindrical space (70), the torque detector (52) detects decreased torque. When the detected torque does not reach the reference torque region, there is a strong possibility that the cake to be discharged from the downstream region (72) may not be sufficiently consolidated, and the speed decrease request signal is output from the comparator (53) to the controller (54). The controller (54) which receives the speed decrease request signal reduces the speed of the drive (25) for a specified time. As a result, the residence time of the raw liquid in the cylindrical space (70) is extended, and the raw liquid undergoes an adequate filtrate dehydration so that the sludge is sufficiently dehydrated. Therefore, the cake having a desired moisture content in a suitably consolidated state is discharged.
Meanwhile, when the moisture content of the cake is lowered, torque detected by the torque detector (52) rises. When the detected torque exceeds the reference torque region, there is a strong possibility that the cake to be discharged from the downstream region (72) may be consolidated excessively, and the speed increase request signal is output form the comparator (53) to the controller (54). The controller (54) which receives the speed increase request signal increases the speed of the drive (25) for a specified time. As a result, the residence time of the raw liquid in the cylindrical space (70) is shortened, and the raw liquid undergoes an adequate filtrate dehydration so that the cake having a desirable moisture content in a suitably consolidated state is discharged.
A seventh aspect of the invention provides a screw press apparatus depending from the third aspect, which further comprises a cleaning pump (55) for supplying cleaning water to the cleaning pipe (34), a drive (25) for driving the screw shaft (6), a torque detector (52) provided for the drive (25), and a control unit (89) for controlling the drive (25) and the cleaning pump (55) in accordance with detected torque detected by the torque detector (52).
According to this arrangement, when the screen (8) is clogged and the load applied to the drive (25) increases, torque detected by the torque detector (52) increases. The control unit (89) is then adapted to control the drive (25) and the cleaning pump (55) in dependence on a variation of detected torque, for restoring the screen (8).
An eighth aspect of the invention provides a screw press apparatus depending from the seventh aspect, in which the control unit (89) has a comparator (53) and a controller (54). The drive (25) comprises a reversible motor, an abnormal torque value is set in the comparator (53). The comparator (53) compares the detected torque with the abnormal torque value, and when the detected torque exceeds the abnormal torque value, the comparator (53) outputs a cleaning request signal to the controller (54), when the controller (54) is not given the cleaning request signal, the controller (54) rotates the drive (25) in the forward direction to have the screw shaft (6) rotate in the forward direction. When the controller (54) receives the cleaning request signal, the controller (54) rotates the drive (25) in the reverse direction for a specified time to have the screw shaft (6) rotate in the reverse direction, and drives the cleaning pump (55) for a specified time to have the cleaning water ejected from the cleaning pipe (34) to the screen (8).
According to this arrangement, in a normal filtering operation in which detected torque by the torque detector (25) is not in excess of the abnormal torque value, the controller (54) does not receive an input of the cleaning request signal.
Accordingly, in a state in which the screen (8) is stopped relative to the frames (3, 4), the screw blade (13) rotates relative to the screen (8), and raw liquid is carried under pressure from the upstream region (71) to the down stream region (72).
When the screen (8) is clogged and the load applied to the drive (25) increases, torque detected by the torque detector (52) increases. When the detected torque exceeds the abnormal torque value, there is a great possibility that the screen may require cleaning. For this reason, the cleaning request signal is output from the comparator (53) to the controller (54). The controller (54) which receives the cleaning request signal rotates the drive (25) in the reverse direction for specified time and drives the cleaning pump (55) for a specified time. Thereby, the screw shaft (6) rotates in the reverse direction, the piston claw (31) is engaged with the claw (28) to prevent the relative rotation of the outside tube (5) with respect to the screw shaft (6), the outside tube (5) and the screen (8) rotate integrally with the screw shaft (6), and sludge in a consolidated state in the cylindrical space (70) is fed back. At the same time, cleaning water is ejected from the cleaning pipe (34) onto the screen (8), and thus the whole peripheral region of the screen (8) is washed and can be reused.
A ninth aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a pump (59) for supplying raw liquid to the cleaning pipe (16), a measuring instrument (56) for measuring a percentage of a solid material in the filtrate flowing out of the screen (8), and a control unit (90) for controlling the pump (59) in accordance with a measured value from the measuring instrument (56).
According to this arrangement, if a cake is stagnant at the downstream region (72) of the cylindrical space (70), increasing the proportion of solid materials in filtrate, the measuring instrument (56) measures an increased value. The control unit (90) is then adapted to control the pump (59) in dependence on a variation of measured value to reduce the supply for supply of raw liquid to the cylindrical space (70). Thereby, the cake stagnation is solved, decreasing the proportion of solid materials in filtrate.
A tenth aspect of the invention provides a screw press apparatus depending from the ninth aspect, in which the control unit (90) has a comparator (57) and a controller (58). A reference value is set in the comparator (57). The comparator (57) compares the measured value with the reference value, and when the measured value exceeds the reference value, the comparator (57) outputs a pressure decrease request signal to the controller (58). When the controller (58) receives the pressure decrease request signal, the controller (58) reduces a force-in pressure of the pump (59).
According to this arrangement, if a cake is stagnant at the downstream region (72) of the cylindrical space (70), increasing the proportion of solid materials in filtrate, the measuring instrument (56) measures an increased value. If the measured value is in excess of the reference value, the amount of stagnant cake may well be excessive, and a pressure decrease request signal is output from the comparator (57) to the controller (58). Given the pressure decrease request signal, the controller (58) makes the pump (59) have a decreased force-in pressure, decreasing the pressure for supply of raw liquid to the cylindrical space (70). Thereby, the cake stagnation is solved, decreasing the proportion of solid materials in filtrate.
An eleventh aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a pump (59) for supplying raw liquid, a supply path (60) for interconnecting the supply pipe (16) and the pump (59), a pressure detector (61) provided in the supply path (60), for detecting an inlet pressure of raw liquid to the cylindrical space (70), and a control unit (91) for controlling the pump (59) in accordance with the inlet pressure detected by the pressure detector (61).
According to this arrangement, with a varying state of raw liquid (sludge and cake) in the cylindrical space (70), the pressure of inflowing raw liquid to the cylindrical space (70) changes, which is detected by the pressure detector (61). The control unit (90) is responsive to a change of the inflow pressure to control the pump (59), decreasing the supply pressure of raw liquid to the cylindrical space (70). Thereby, raw liquid in the cylindrical space (70) enters a stable state, rendering the filtration process stable.
A twelfth aspect of the invention provides a screw press apparatus depending from the eleventh aspect, in which the control unit (91) has a comparator (62) and a controller (63). A reference pressure region having a specified range is set in the comparator (62). The comparator (62) compares the inlet pressure with the reference pressure region, and when the inlet pressure exceeds the reference pressure region, the comparator (62) outputs a pressure decrease request signal to the controller (63), and when the inlet pressure does not reach the reference pressure region, the comparator (62) outputs a pressure increase request signal to the controller (63). When the controller (63) receives the pressure decrease request signal, the controller (63) decreases a force-in pressure of the pump (59) a for specified time, and when the controller (63) receives the pressure increase request signal, the controller (63) increases the force-in pressure of the pump (59) for a specified time.
According to this arrangement, in the case where the sludge in the cylindrical space (70) is not sufficiently dehydrated and it insufficiently becomes a cake, the inlet pressure of the raw liquid into the cylindrical space (70) detected by the pressure detector (61) is lowered. When the inlet pressure does not reach the reference pressure region, there is a strong possibility that a cake in a desirably consolidated state is not discharged. For this reason, the pressure increase request signal is output from the comparator (62) to the controller (63). The controller (63) which receives the pressure increase request signal increases the force-in pressure of the pump (59) for a specified time. As a result, the supplying amount of the raw liquid into the cylindrical space (70) increases, and the pressure in the cylindrical space (70) rises, and the sludge is sufficiently dehydrated to be concentrated so that the cake in the desirably consolidated state is discharged.
Meanwhile, in the case where the sludge in the cylindrical space (70) is abruptly dehydrated and the cylindrical space (70) is filled with the cake, the inlet pressure of the raw liquid into the cylindrical space (70) detected by the pressure detector (61) rises. When the inlet pressure exceeds the reference pressure region, there is strong possibility that the raw liquid is excessively fed because the cylindrical space (70) is filled with the cake. For this reason, the pressure decrease request signal is output from the comparator (62) to the controller (63). The controller (63) which receives the pressure decrease request signal reduces the force-in pressure of the pump (59) for specified time. As a result, the supplying amount of the raw liquid into the cylindrical space (70) is reduced, and thus deterioration in the throughput capacity due to the excessive supplying of the raw liquid is prevented previously.
A thirteenth aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a cake discharge hole (96) for a cake to be pushed therethrough out of the cylindrical space (70), an air cylinder (23) fixed to the second frame (4), an air cylinder (23) connected to a shaft (23a) of the air cylinder (23) and adapted for forward and backward movements to change the open degree of the cake discharge hole (96), a detector (100) provided for the air cylinder (23), for detecting the open degree, an air supply path (101) connected to the air cylinder (23), a regulator valve (102) provided in the air supply path (101), a pilot valve (103) for changing a set air pressure of the regulator valve (102), and a control unit (104) for operating the pilot valve (103) in accordance with a detected value from the detector (100).
According to this arrangement, a cake is discharged through the cake discharge hole (96), from the downstream region (72) of the cylindrical space (70). The open degree of the cake discharge hole (96) is changed by the presser (21).
With a varying condition of cake, the pressing force from the cake to the presser (21) changes, and the open degree of the cake discharge hole (96) is changed, and the detection value from the detector (100) is varied. The control unit (104) is then adapted for operating the pilot valve (103) in dependence on a change amount of the open degree (as a variation of the detected value), to have a switched set air pressure of the regulator valve (102), increasing or decreasing the pressure in the air cylinder (23). Thereby, the presser (21) moves, the open degree of the cake discharge hole (96) is changed, the variation in thickness of the cake to be discharged is suppressed, and a cake of a desirable thickness is discharged in a stable manner.
A fourteenth aspect of the invention provides a screw press apparatus depending from the thirteenth aspect, in which the control unit (104) has a comparator (105) and a controller (106). A standard open degree is set in the comparator (105). The comparator (105) compares the detected value with the standard open degree, and when the detected value exceeds the standard open degree, the comparator (105) outputs a pressure increase request signal to the controller (106), and when the detected value does not reach the standard open degree, the comparator (105) outputs a pressure decrease request signal to the controller (106). When the controller (106) receives the pressure increase request signal, the controller (106) increases the set air pressure of the regulator valve (102), and when the controller receives the pressure decrease signal, the controller (106) decreases the set air pressure of the regulator valve (102).
According to this arrangement, when the cake is hardened, a pressing force from the cake to the presser (21) increases, the degree of opening of the cake discharge hole (96) increases, and the detected value from the detector (100) increases. When the detected value exceeds the standard open degree, there is a strong possibility that the thickness of the cake to be discharged may be remarkably increased, and the pressure increase request signal is output from the comparator (105) to the controller (106). The controller (106) which receives the pressure increase request signal operates the pilot valve (103) to increase the set air pressure of the regulator valve (102). As a result, the presser (21) moves, and the increase in degree of opening of the cake discharge hole (96) is suppressed, and the cake having a uniform thickness is discharged.
Meanwhile, when the cake is softened, a pressing force from the cake to the presser (21) is decreased, and the degree of opening of the cake discharge hole (96) is decreased so that the detected value from the detector (100) decreases. When the detected value does not reach the standard open degree, there is a strong possibility that the thickness of the cake to be discharged may be decreased remarkably, and the pressure decrease request signal is output from the comparator (105) to the controller (106). The controller (106) which receives the pressure increase request signal operates the pilot valve (103) to reduce the set air pressure of the regulator valve (102). As a result, the presser (21) moves so that the reduction in degree of opening of the cake discharge hole (96) is suppressed and the cake having a uniform thickness is discharged.
A fifteenth aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a cake discharge hole (96) for a cake to be pushed therethrough out of the cylindrical space (70), an air cylinder (23) fixed to the second frame (4), a presser (21) connected to a shaft (23a) of the air cylinder (23) and adapted for forward and backward movements to change the open degree of the cake discharge hole (96), a detector (100) provided for the air cylinder (23), for detecting the open degree, and a control unit (104) for controlling the drive (25) in accordance with the detected value from the detector (100).
According to this arrangement, a cake is discharged through the cake discharge hole (96), from the downstream region (72) of the cylindrical space (70).
If the moisture content of cake is varied, the pressing force from the cake to the pressure (21) varies, causing the open degree of the cake discharge hole (96) to change, and the detection value from the detector (100) is changed. The control unit (104) is then adapted to control the drive (25) in dependence on a change of the open degree (as a change of the detection value), for increasing or decreasing the transfer speed of raw liquid in the cylindrical space (70) to supress the variation in moisture content of the cake. The moisture content of the cake to be discharged is thereby rendered stable.
A sixteenth aspect of the invention provides a screw press apparatus depending from the fifteenth aspect, in which the control unit (104) has a comparator (105) and a controller (106). The drive (25) comprises a variable speed motor. A reference open degree is set in the comparator (53). The comparator (53) compares the detected value with the reference open degree, and when the detected value exceeds the reference open degree, the comparator (53) outputs a speed increase request signal to the controller (106), and when the detected value does not reach the reference open degree, the comparator (53) outputs a speed decrease request signal to the controller (106). When the controller (106) receives the speed increase request signal, the controller (106) has the drive (25) increase in speed, and when the controller (106) receives the speed decrease request signal, the controller (106) has the drive (25) decrease in speed.
According to this arrangement, when the cake is hardened and the moisture content is lowered, a pressing force from the cake to the presser (21) increases, the degree of opening of the cake discharge hole (96) increases, and the detected value from the detector (100) increases. When the detected value exceeds the standard open degree, there is a strong possibility that the thickness of the cake may be remarkably increased, and the speed increase request signal is output from the comparator (105) to the controller (106). The controller (106) which receives the speed increase request signal has the drive (25) increase in speed, for increasing the transfer speed of raw liquid in the cylindrical space (70) to raise the moisture content of cake. The moisture content of the cake to be discharged is thereby stabilized to a constant state.
Meanwhile, when the cake is softened and the moisture content rises, a pressing force from the cake to the presser (21) is decreased, and the degree of opening of the cake discharge hole (96) is decreased so that the detected value from the detector (100) decreases. When the detected value does not reach the standard open degree, there is a strong possibility that the thickness of the cake may be increased remarkably, and the speed decrease request signal is output from the comparator (105) to the controller (106). The controller (106) which receives the pressure increase request signal has the drive (25) decrease in speed, for delaying the transfer speed of raw liquid in the cylindrical space (70) to reduce the moisture content of cake. The moisture content of the cake to be discharged is thereby stabilized to a constant state.